Body fluid can be divided into din and Ye. Though both of them come from the food taken, and are formed through the transportation and transformation function of the spleen and stomach, they differ in their properties, function and distribution. Generally, din refers to the thin and clear body liquid with strong mobility, which scatters in the skin, muscles and orifices and is able to permeate into the blood vessels to function moistening. Ye refers the turbid body fluid with weak mobility which pours into the joints, viscera, brain and marrow to function nourish. Both din and Ye can change into each other, therefore they are generally termed din Ye (body fluid).

Body fluid is a general term for all normal liquid in the body, including the intestinal juice and normal excretion of the viscera, tissues and organs, such as gastric juice, intestinal juice and nasal juice, tears etc. Like qi and blood, body fluid is the substance to make up the body and maintain the life activities of the body.

two. Formation, Distribution and Excretion of Body FluidThe formation, distribution and excretion of body fluid are the complicated physiological processes involving in a series of physiological functions of many viscera.

1. FormationBody fluid derives from the drink and food. It's formed through the digestion function of the stomach, separating refine substance from the dross substance of the small intestinal function, and the transporting function of the spleen, So it relates to the physiological activities of the stomach, small intestine and spleen that body fluid is abundant or not.

2. DistributionDistribution of body fluid is accomplished mainly by the joint functions of the spleen, lung, kidney, and triple-jiao.

The spleen's action on the body fluid distribution: By its transportation and transformation function, the spleen on one hand transfer the fluid up to the lung; on the other hand, it distributes the fluid throughout the body, which is the function of "distributing the essence" of the spleen.

The lung's action on the body fluid distribution: By its dispersing function, the lung distributes the fluids to all parts of body, externally to the skin and hair. By its depurative descending function, on the other hand, the lung sends the fluid downward to perform nourishing and moistening function of body fluid.

The evaporating and transformative functions of the kidney control the metabolism of body fluid. All the fluid in the body will distribute throughout the body via the functions of evaporating and sending up the clear and sending downward of the turbid.

Triple-jiao is the passage for the distributing of body fluid. Via this passage way, the body fluid distributes throughout the body, and circulates constantly with qi ascending, descending, exiting and entering.